Changes in Version 2.5-0

  o Enhanced vignette("sandwich-CL", package = "sandwich") by better describing
    the background of clustered covariances and being more precise in the mathematical
    notation. Documentation for the new features (see below, e.g., the formula cluster
    specification and the vcovBS() methods) has been added.

  o In vcovCL(), vcovPL(), vcovPC(), and vcovBS(), the "cluster" argument (and
    potentially also "order.by") can be specified by a formula - provided that
    expand.model.frame(x, cluster) works for the model object x.
    
  o The "cluster" and/or "order.by" are processed accordingly if observations
    were dropped in the NA processing of the model object x (provided x$na.action
    is available).
    
  o New dedicated vcovBS() method for "lm" objects that (a) provides many more
    bootstrapping techniques applicable to linear models (e.g., residual-based
    or wild bootstrap), (b) computes the bootstrap coefficients more efficiently
    with lm.fit() or qr.coef() rather than update().

  o New dedicated vcovBS() method for "glm" objects that uses "xy" bootstrap
    like the default method but uses glm.fit() instead of update() and hence
    is slightly faster.

  o All vcovBS() methods (default, glm, and lm) facilitate parallel bootstrapping
    by changing the "applyfun" from the default lapply(). By setting "cores"
    parallel::parLapply (on Windows) or parallel::mclapply() (otherwise)
    are used.

  o Default handling of missing parameter estimates in vcovBS() changed
    from "everything" to "pairwise.complete.obs" and allow modification
    of cov(..., use = ...). This is relevant if not all parameters can be
    re-estimated on the bootstrap samples, e.g., for dummy variables of
    relatively rare events.

  o Fix of a bug in vcovHC.mlm (reported by James Pustejovsky). The off-diagonal
    values of the vcovHC were computed without preserving the sign of the
    underlying residuals. This issue did not affect the diagonal because
    the underlying cross product amounts to squaring all values - but it does
    matter for the off-diagonal. Also, type="const" was disabled in this
    scenario and vcov(...) is simply used instead of vcovHC(..., type = "const").

  o Bug fix in vcovCL/meatCL for multi-way clustering (reported by Brian Tsay).
    If patterns of levels in one clustering variable also occured in another
    clustering variable, their interactions were sometimes not computed
    correctly.

  o In vcovCL() for multi-way clustering without cluster adjustment, all
    cluster adjustment factors are omitted entirely. In previous versions they
    were scaled with (Gmin - 1)/Gmin, where Gmin is the minimal number of
    clusters across clustering dimensions.
  
  o meatHC() and meatHAC() now pass their "..." argument to estfun(), just
    as meatCL(), meatPL(), and meatPC() do as well.


Changes in Version 2.4-0

  o Various flavors of clustered sandwich estimators in vcovCL(), panel
    sandwich estimators in vcovPL(), and panel-corrected estimators a la
    Beck & Katz in vcovPC(). The new vignette("sandwich-CL", package = "sandwich")
    introduces all functions and illustrates their use and properties.

  o The new function vcovBS() provides a basic (clustered) bootstrap
    covariance matrix estimate, using case-based resampling.


Changes in Version 2.3-4

  o In meatHAC(), bwAndrews(), and bwNeweyWest() it is now assured that
    the estfun is transformed to a plain matrix. Otherwise for time series
    regression with irregular zoo data, the bandwidth estimation might
    have failed.

  o In meatHC() it is now assured that the residuals are zero in observations
    where all regressors and all estimating functions are zero.


Changes in Version 2.3-3

  o Now the default methods of vcovHC() and vcovHAC() are also correctly
    registered as S3 methods in the NAMESPACE.

  o Corrected errors in Equation 3 of vignette("sandwich"). The equation
    incorrectly listed the error terms "u" instead of the observations "y"
    on the right-hand side (pointed out by Karl-Kuno Kunze).


Changes in Version 2.3-2

  o sandwich(), vcovHC(), and vcovHAC() did not work when models were
    fitted with na.action = na.exclude because the estfun() then (correctly)
    preserved the NAs. This is now avoided and all functions handle the
    na.exclude case like the na.omit case. (Thanks to John Fox for spotting
    the problem and suggesting the solution.)


Changes in Version 2.3-1

  o The estfun() methods for "survreg" and "coxph" objects incorrectly
    returned the unweighted estimating functions in case the objects
    were fitted with weights. Now the weights are properly extracted
    and used.


Changes in Version 2.3-0

  o Updated Depends/Imports: Package "zoo" is only in Imports now.


Changes in Version 2.2-10

  o Added estfun() and bread() methods for ordered response models
    from MASS::polr and ordinal::clm.

  o Added output of examples and vignettes as .Rout.save for
    R CMD check.


Changes in Version 2.2-9

  o Added convenience function lrvar() to compute the long-run
    variance of the mean of a time series: a simple wrapper
    for kernHAC() and NeweyWest() applied to lm(x ~ 1).

  o lm/mlm/glm models with aliased parameters were not handled
    correctly (leading to errors in sandwich/vcovHC etc.), fixed
    now.

  o An improved error message is issued if prewhitening in vcovHAC()
    cannot work due to collinearity in the estimating functions.


Changes in Version 2.2-8

  o fixed a bug in bwNeweyWest() for "mlm" objects that only have
    an intercept.


Changes in Version 2.2-7

  o HC4m and HC5 estimators, as suggested by Cribari-Neto
    and coauthors, have been added to vcovHC() and related
    functions.


Changes in Version 2.2-6

  o bug fix in estfun() method for "survreg" objects


Changes in Version 2.2-5

  o estfun() methods for "hurdle"/"zeroinfl" objects can now
    handle multiple offset vectors (if any)


Changes in Version 2.2-4

  o new vcovHC() method for "mlm" objects. This simply
    combines the "meat" for each individual regression and combines
    the result.


Changes in Version 2.2-3

  o new bread() method for "mlm" objects.


Changes in Version 2.2-2

  o updates in estfun() methods for hurdle/zeroinfl objects.


Changes in Version 2.2-1

  o documentation enhancements for new Rd parser.


Changes in Version 2.2-0

  o added/enhanced bread() and estfun() methods for "rlm" 
    and "mlogit" objects (from MASS and mlogit, respectively).
    
  o made vcovHC() and vcovHAC() generic with previous function
    definitions as default methods.    

  o updated vignettes (in particular using the more convenient
    tobit() interface from the AER package).


Changes in Version 2.1-0

  o added bread() and estfun() methods for "hurdle"/"zeroinfl"
    objects as computed by hurdle()/zeroinfl() in
    package "pscl".
  
  o fixed bread() and estfun() methods for negative binomial
    "glm" objects: now dispersion = 1 is used.
  

Changes in Version 2.0-3

  o bread() method for "lm" objects now calls summary.lm()
    explicitely (rather than the generic) so that it also
    works with "aov" objects.
  

Changes in Version 2.0-2

  o Added new vcovOPG() function for computing the outer
    product of gradients estimator (works for maximum
    likelihood estfun() methods only).
  
  o Scaled estfun() and bread() method for "glm" objects
    by dispersion estimate. Hence, this corresponds to
    maximum likelihood and not deviance methods.
  

Changes in Version 2.0-1

  o Minor fix to bwAndrews() so that it can be easily used
    in models for multivariate means.
  

Changes in Version 2.0-0

  o A paper based on the "sandwich-OOP" vignette was accepted
    for publication in volume 16(9) of Journal of Statistical
    Software at
      http://www.jstatsoft.org/
  
  o A NAMESPACE was added for the package.
  

Changes in Version 1.9-0

  o The vignette "sandwich-OOP" has been revised, extended and
    released as a technical report.
    
  o Several estfun() methods and some of the meat() functions have
    been enhanced and made more consistent.


Changes in Version 1.1-1

  o estfun() methods now use directly the model.matrix() method
    instead of the terms() and model.frame() methods.


Changes in Version 1.1-0

  o sandwich is made object-oriented, so that various types
    of sandwich estimators can be computed not only for "lm"
    models, but also "glm", "survreg", etc.
    To achieve object orientation this various changes have
    been made: a sandwich() function is provided which needs
    a bread and a meat matrix. For the bread, a generic bread()
    function is provided, for the meat, there are meat(),
    meatHC() and meatHAC(). All rely on the existence of a
    estfun() method.
    
  o vcovHC() and vcovHAC() have been restructured to use
    sandwich() together with meatHC() and meatHAC(), respectively.
    
  o A new vignette "sandwich-OOP" has been added, explaining
    the new object-orientation features.
    
  o Various methods to bread() and estfun() have been added,
    particularly for "survreg" and "coxph".
    
